Method of sending information through a tree and ring topology of a network system

ABSTRACT

The method is for sending information through a topology. A first and second node each having a first node having a first access port, a second access port and a first uplink connected to a first router and a second router, respectively. A third node is provided that has a first access port and a first uplink, the first uplink of the third node being connected to the second access port of the first node. A first packet is sent via the first access port to the second node. The second node adds a first port number to a tag of the first packet and sends the first packet via the first uplink of the second node to the first access port of the first node. The first node receives the first packet via the first access port of the first node. The first node adds the first port number to the tag and adds a first port number of the first access port of the first node to the tag. The first node sends the first packet via the first uplink of the first node to a first router.

PRIOR APPLICATION

This is a continuation-in-part patent application of U.S. patentapplication Ser. No. 10/707,916, filed 23 Jan. 2004.

TECHNICAL FIELD

The method of the present invention relates to sending informationthrough a tree topology or a ring topology of a network system.

BACKGROUND AND SUMMARY OF INVENTION

Metro networks are often organized in two levels including metro accessand metro core systems. Metro access networks are deployed near the endcustomer while metro core networks aggregate several access networksdeployed in different parts of the metro area. The metro core systemsalso host the gateway(s) to the wide area backbone network. Currentlythe dominating technology to connect individual customers and businessesto the Internet is a leased 1.5 or 2.0 Mbps TDM circuits from thecustomer premises to the provider edge node, that is, router or a switchlocated in the point-of-presence (POP). The edge equipment is populatedwith channelized TDM interface cards. This TDM circuit, with limited andrelatively expensive capacity, is a bottleneck. The access circuit isprovisioned separately from the provisioning of the network service,such as an IP service, leading to high operational overhead. Whenseveral circuits are aggregated in the TDM access network, statisticalsharing of capacity is not possible due to the fixed nature of TDMcircuits. Statistical multiplexing of the traffic can occur only firstafter the traffic reaches the router. The channelized TDM interfacesinclude complex hardware that monitors each circuit individually butmakes line cards expensive.

The capacity bottleneck of the TDM system may be avoided by migrating toa high-capacity packet-based access infrastructure, such as Ethernet.Ethernet equipment is low cost, high capacity, and widely deployed inthe industry. Ethernet switches forwards packets based on thedestination address. Ethernet switches are intended for friendlyenterprise environments and include a number of automatic features inorder to ease the installation and operation of the network. However,these automatic features become problematic in large scale operatorenvironments. The automatic features do not scale to largeinfrastructures and needs sometimes to be disengaged to increasesecurity. This requires manual configuration of possibly a large numberof individual units. One specific example of an automatic feature ofEthernet switches is that they dynamically learn each unique sourceaddress of the packets received in order to optimize the forwarding oftraffic. It is sometimes necessary to disengage this learning process toprevent customers from being able to communicate directly with eachother without going through a service provider. In summary, problemswith basic Ethernet switches include: no support for customerseparation; low degree of security due to the fact that cross trafficdirectly between end-customers is allowed; dynamic address learning mayopen up for DoS attacks; and requires distributed element management andservice creation due to the fact that a potential large set ofdistributed units needs to be configured and managed; and the standardbased Spanning Tree Protocol (STP) based restoration is slow.

The method of the present invention provides a solution to theabove-outlined problems. More particularly, the method is for sendinginformation through a topology. A first and second node each having afirst access port, a second access port and a first uplink connected toa first router and a second router, respectively. A third node isprovided that has a first access port and a first uplink, the firstuplink of the third node being connected to the second access port ofthe first node. A first packet is sent via the first access port to thethird node. The third node adds a first port number to a first sectionof a tag of the first packet and sends the first packet via the firstuplink of the third node to the first access port of the first node. Thefirst node receives the first packet via the first access port of thefirst node. The first node shifting the first port number to a secondsection of the tag and adds a first port number of the first access portof the first node to the first section of the tag. The first node sendsthe first packet via the first uplink of the first node to a firstrouter.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a schematic illustration of node units in an access network;

FIG. 2 is a schematic illustration of two node units connected in atandem mode;

FIG. 3 is a schematic illustration of a tandem node abstraction;

FIG. 4 is a schematic illustration of a frame with a shim header;

FIG. 5 is a schematic illustration of VLAN packet with nibbles;

FIG. 6 is a schematic illustration of tree mode addressing;

FIG. 7 is a schematic illustration of rules of tree mode addressing;

FIG. 8 is a schematic illustration of ring mode addressing;

FIG. 9 is a schematic illustration of ring mode addressing;

FIG. 10 is a schematic illustration of rule of ring mode addressing;

FIG. 11 is a schematic illustration of port number shifting in ingresstraffic;

FIG. 12 is a schematic illustration of port number removal in egresstraffic;

FIG. 13 is a schematic illustration of an unprotected tree topology ofthe present invention;

FIG. 14 is a schematic illustration of a redundant daisy-chain topologyof the present invention;

FIG. 15 is a schematic illustration of an unprotected point-to-pointtopology of the present invention;

FIG. 16 is a schematic illustration of a redundant tree topology havinga tandem node of the present invention;

FIG. 17 is a schematic illustration of a redundant tree topology havinga plurality of tandem nodes of the present invention;

FIG. 18 is a schematic illustration of a redundant ring topology havinga tandem node of the present invention; and

FIG. 19 is a schematic illustration of a redundant point-to-pointtopology of the present invention.

DETAILED DESCRIPTION

In general, the method of the present invention includes steps forsending information up and down a tree topology of nodes in a network.The method also covers the steps of sending information in a ringtopology of nodes. The method includes steps of adding a tag and portnumbers when the packet moves upwardly in a tree topology towards edgeequipment such as a router or a switch, i.e. in an ingress direction, sothat each node shifts previous port numbers and adds a port numberbefore forwarding the packet. When the packet moves from a router orswitch downwardly in the tree topology, i.e. in an egress direction,each node removes a port number, such as the port number of thedeparture port, from the tag and shifts the subsequent port numberswithin the tag. The invention is not limited to shifting the portnumbers between nibbles. It is also possible to merely add and removeport numbers and other identification information from the nibbleswithout shifting such information.

With reference to FIG. 1, the physical topology 230 may include Marvinnode units 232, 234. A tree structure may be used to aggregate thecustomer traffic in several steps towards a hub node. A daisy-chain ofMarvin multiplex units 232, 234 can be used to simplify the build outwhen a tree is unsuitable or to reduce the amount of fiber or copperlinks as well as the number of router or switch interfaces. The units232, 234 can be used to connect and merge a plurality of customer lineswhile keeping each customer's traffic separate with tags so the trafficstreams are not mixed up. For example, each unit may have ten customerports and two uplinks. The units 232, 234 may have the characteristicsof receiving and sending Ethernet frames and the units only switchinformation between the access ports and the network ports and viceversa but not between different access ports. The tags may be used todistinguish the traffic from and to the customers so that a virtualinterface in the provider edge equipment may be set up for eachcustomer. Preferably, the tags are of a type that is currently used bymany provider edge equipments to make the implementation easy. Asexplained in detail below, when untagged traffic is coming from acustomer the Marvin node units add the tags before the traffic is sentto other nodes or to the router. Similarly, when traffic going from theprovider edge equipment to the customer, tag segments are removed andshifted as the packet moves towards the customer. The provider edgeequipment may in turn be connected to an IP network or any othersuitable network.

Many different access network service architectures may be used. Thearchitectures may be based of the number of redundant connections to themetro core network and to the customer site. Single and dual connectionsprovide four possible combinations including a single network that has asingle customer connected thereto. In a single-network-single-customerarchitecture, the access network is attached to the metro core via oneconnection and the customer is connected to the access subsystem via oneconnection. All traffic transmitted from the network core via the accesssystem is delivered without duplication to the customer and vice versa.All redundancy and restoration mechanisms are hidden within the accesssubsystem. It is impossible in this architecture to protect theattachment links or attachment nodes.

Another situation is a dual network with a single customer attachedthereto. The access network is attached to the metro core via twoindependent connections and the customer is connected to the accesssubsystem via one connection. In this way, two provider edge nodes maybe connected to the access network so that one provider edge node may bethe back-up for the other in case the first one malfunctions. Alltraffic transmitted from the network core via any of the two metro coreattachment links are forwarded to the customer. Traffic from thecustomer is forwarded to both of the two metro core access links if theprovider edge equipment is capable of filtering the information in orderto avoid duplication (i.e. IP routers). In other environments, such asswitched Ethernet, ingress traffic is only sent via one of the two metrocore access links. This additional filtering is provided by the Marlinnode attaching to the metro core. It is possible in this architecture toprotect the attachment links or attachment nodes, but it requiresadditional functionality in the metro core system or in the customersystem. The requirements may be fulfilled by specific redundancymechanisms such as VRRP, HSRP or generic dynamic routing protocols suchas OSPF. VRRP and HSRP only effects the metro core system, OSPF requiresalso the customer to participate in the protection procedure.

Another classification is a single-network with a dual-customer attachedthereto. The access network is attached to the metro core via oneconnection and the customer is connected to the access subsystem viadual connections. All traffic transmitted from the network core via theaccess system is delivered without duplication to either of the customerconnections. Two modes of this system are possible. Either the customerdelivers one copy of each frame to both of the attachment connection orthe customer delivers a single copy to one of the attachmentconnections. In both cases the access network guarantees to deliver thetraffic without duplication. If the customer choose to send traffic toonly one of the access links it requires the customer to interact eitherwith the access system itself or the metro core system to accomplishrestoration in case of failures.

The last classification includes a dual-network with a dual-customerattached thereto. The access network is attached to the metro core viadual connections and the customer is also connected to the accesssubsystem via dual connections.

A basic requirement for all types of restoration mechanisms is thepresence of redundant resources. One common model is to use one specificresource as primary and protect it by a back-up or stand-by resource ofthe same type. One resource can be the back-up for a number of primaryresources. The types of resources that can be duplicated in accesssystems built with Marlin units are communication links and Marlinnodes. The communication link includes optical as well as electricalones. To provide a high degree of redundancy, the duplicated linksshould be located in different cables in order to achieve physicallydifferent communication paths. Nodes, such as Marlin units, can beduplicated in order to protect against nodes failures and to provide amechanism to perform up-grades and maintenance on these withoutdisturbing the service delivery.

The node unit of the present invention implements a multiplexing stageto be used in access networks connecting to routers and switches. Thesmall size and low per port and per unit cost allows the unit to belocated very close to customers or inside the customer premises.

All multiplexing, de-multiplexing in the system of the present inventionmay be based on standard 802.1q tagged Ethernet frames. Future productsmay utilize other schemes such as MPLS or IP tunneling. The generalmechanisms are however the same allowing different implementationoptions when needed. With three levels, or less, of multiplexing asingle VLAN tag may contain the full path information such as sourceroute information, only placing a requirement of being able to handle asingle tag on the router or switch. The logical topology of the accesssystem is preferably hub-and-spoke, but the physical topologies can bedaisy-chains, rings and trees possibly with multiple redundant nodesdistributed in the physical topology.

Preferably, the supported link mode is full duplex only for TX linkssince FX links are always full duplex. This allows for simplermanagement of the access network independent of link types. The usage offull duplex links can also helps maintaining QoS and simplifiesconfiguration and error localization in Marlin node networks.

Each node unit may have ten access ports so that each access port may beused to connect a customer or another Marlin node unit. Of course, thenode units may have more or fewer access ports. All ingress dataarriving on the access port are tagged with the corresponding portnumber and then forwarded to the network port(s). Access ports areisolated from each other and direct communication, without passing theroot node, between two access ports is not possible. This increasessecurity and prevents unwanted cross-traffic.

Preferably, there are two uplink network ports in each node unit. Thenetwork ports are used to connect to a switch, router or another Marlinunit. Packets arriving on the network port are assumed to be tagged withthe outgoing access port number that the packet is destined for. Asoutlined in detail below, the frames are sent out on the access port andthe port routing information in the tag is removed. If the remaining tagis 0, indicating that the last hop in Marlin network has been reached,the complete tag is removed, as explained in detail below.

The node unit may be managed via any of the network ports or a dedicatedmanagement port such as the AUX port. One purpose of the AUX port is toallow a management station to be attached to the Marlin node unit whenboth of the network ports are used as uplinks. The AUX port is a 10/100Ethernet port only used to connect an external computer running a Marlinsoftware with a remote CLI process or other management software, to theunit for local debugging in the field or to directly connect a Marlinunit controller (MUC).

The Marlin node units, such as the M1000 products, may use optical fiberinterfaces for some of the ports. SFP cages are used and may bepopulated with SFP modules with different ranges and modes. The networkports are made of copper and fiber, one RJ45 copper connector and oneSFP fiber module per port. Preferably, only one of them is active at atime. The access ports are copper for M1000T and fiber for M1000F.

Preferably, the M1000F has ten 100 Mbps fiber optical access interfaceports, two dual network ports and one AUX port. Each access port is asmall form factor with a pluggable optical transceiver (SFP) socket thataccepts modules. Each of the two network ports of the M1000F is bothcopper 10/100/1000 Mbps and fiber 100/1000 Mbps Ethernet ports. Thenetwork SFP cages can be populated with 100 Mbps or 1000 Mbps SFPmodules. When both fiber and copper interfaces are connected theselected default interface is active while the other interface isdisabled.

Two redundant fans are located on the right side of the unit. Each ofthe fans provides enough airflow for cooling. The fans are notaccessible from the outside of the unit. The fan status can be monitoredby the management system and if a fan fails an event notificationmessage may be generated.

The Optional Management Card (OMC) is an internal CPU card that providesadditional services to the base M1000 system. The OMC card runs a customnetwork operation system with SNMP agent(s), a command line interface(CLI) and other management processes.

To simplify management of a Marlin system, and minimize the possibilityof configuration errors, automatic topology detection and configurationis available. One purpose of the automatic topology detection is toallow an operator or a management station to execute an automatictopology detection protocol and gather the complete physical topologymap without prior configured knowledge about the topology.

The basic mechanism used to collect information about node status andtopology is the soon to be standard EFM OAM Information PDUs such asIEEE802.3ah-Ethernet in the first mile (EFM). Preferably, a Marlin unitwill always terminate untagged OAM Information PDUs received via thenetwork ports and reply with a vendor specific extended EFM OAMInformation PDU. With this mechanism the node closest to the managementstation can be probed and configured. With the closest unit configuredand configured to a known state it is possible to probe further in thenetwork topology.

Probing down a tree topology may be done top-down. When the first unitis probed and configured the units connected to the access ports can beprobed and then configured. For example, probing of the unit connectedto port 3 of the top unit is done with Ethernet frames containing a tagwith value 0x003. The first unit removes the tag before sending theprobe to port 3 untagged. By probing all access ports with active linksin the tree hierarchy all units can be detected and configured.

Probing for ring topologies may mean that probe messages are sent out onnetwork ports (U1 or U2) to investigate if the network port of anotherMarlin is connected. To generate an untagged probe to be sent out on anetwork port of a specific node located somewhere in the infrastructure,the probe is tagged in such a way that it arrives to the node with a tag0x00E. If the probe tagged with 0x00E arrives on U1, the untagged probeis forwarded on U2. When the untagged probe response later arrives fromU2 it is tagged with 0x000E and forwarded via U1. Tree probing requirestwo mechanisms to be present in a node. Firstly, probe messages taggedwith 0x00E and arriving via one network port are transmitted untaggedvia the other network port. Secondly, untagged probe reply messagesarriving via one network port are tagged with 0x00E and transmitted viathe other network port. Probe messages are implemented as standard EFMOAM Information PDUs. Probe reply messages are implemented as vendorspecific extended EFM OAM Information PDUs. In the case a Marlin unitcontroller is present at the AUX port or an OMC port it will beresponsible for all probing and the messages will always pass throughthe unit controller. There are two cases how ring probing is donedepending on the mode the known unit is configured to. Firstly, if aMarlin unit is in tree mode and it receives an OAM packet addressed to0x00E from a network port, it will remove the tag and send it out on theother network port for probing. If another unit is daisy chain connectedto this port it will process the probe and reply back untagged. Thefirst unit recognizes that it is a probe reply and tag the frame withport-id 0x00E and the forward it the other network port. Secondly, if anode is in ring mode and it receives a packet addressed 0x0rE, whereinr=ring node number for the unit, from a network port, it will remove thetag and send it out on the opposite network port. If another unit isdaisy chain connected to this port it will process the probe and replywith an untagged. The first unit recognizes that it is an OAM probereply and tags the frame with port-id 0x0rE and forwards it to the othernetwork port. In this way, it is possible to probe and configure theunits that are connected in daisy chain in the same way as for treetopologies.

FIG. 2 shows two Marlin units 242, 244 of a system 240 that may beconnected in tandem to provide redundancy. Of course, the Marlin units242, 244 do not have to be connected in tandem. When connected in tandemthe U2 network ports 246, 248 of the two Marlin units or nodes 242, 244are connected together via a U2 link 250 and the access ports 252, 254are grouped in pairs such that access ports (i), wherein (i)=252/254(1);252/254(2) : : : ; 252/254(10)), of the two units 242, 244 belong to thesame group. The Marlin unit 242 may have a U1 link 258 and the Marlinunit 244 may have a U1 link 260. The index of the port group may be thesame as the index of the ports. The behavior of the tandem nodes 242,244 on a per port basis is described below. Ingress traffic from acustomer C is forwarded to both the U1 and U2 links to provideredundancy. If the tandem node is connected to an IP network via one orseveral IP routers, the routers ensures that the same message is notsent twice to the IP network. If the tandem node is connected to aswitched Ethernet via one or several Ethernet switches, it is theresponsibility of the tandem node to assure that no duplicated messagesare sent into the attachment switches.

The egress traffic of the tandem node 242 may, for example, be receivedvia the network port links U1 of the tandem node 242, i.e. the U1network ports of one of the constituent Marlin nodes, and is forwardedto one of the access ports of a port group determined by the tag of thereceived traffic. If traffic is simultaneously received via the othernetwork port of the tandem node, that is, the port U1 of the otherconstituent Marlin node and is tagged with the same value, that trafficis forwarded to one of the access ports in the same port group, so itdoes not matter if the tagged traffic comes via one or the other networkports of the tandem node. The routing of traffic within the tandem nodes242, 244 depends on the tag in same manner as in an individual Marlinnode so that frames tagged with 0xXX3 is forwarded to one of the portsin port group 3.

The ingress traffic received via one of the access ports 252, 254 in aport group is forwarded to both of the network ports U1 of the tandemnodes 242, 244. The ingress traffic received via the other port in thegroup is preferably dropped.

Thus, the behavior of a tandem mode may be the same as the behavior of anormal Marlin node if the port groups are considered as abstract portsso that the identity of the individual ports within a port group isdisregarded.

As best shown in FIG. 3, internally the tandem node 256 may consist oftwo Marlin units 242, 244 with connected U2 ports and two U1 ports 258,260. Port group (i) of the tandem node 256 may consist of access port(i) of the two constituent units 242, 244. Each of the two Marlin units242, 244 operates in a tandem mode. When in the tandem mode, a Marlinunit can be in one of two tandem states on a per access port basis,including active and stand-by states. The state of the Marlin unitrelative to a first access port may be active while the Marlin unit maybe in a stand-by state relative to a second access port. In other words,the state of the Marlin units is in relation to the access ports. Whenthe Marlin unit is in the active state, relative to the access port (p),the Marlin unit operates exactly in the same manner as an ordinaryMarlin unit i.e. it forwards data tagged with 0xp received from any ofits network ports to port (p) and forwards all ingress traffic receivedvia access port (p) to both of its network ports 258, 260. When in thestand-by state, relative to the access port (p), the Marlin unitby-passes all traffic tagged with 0xXXp received via U1 ports 258 or 260unmodified to U2 for egress traffic and vice versa for ingress traffic.Furthermore, ingress traffic received via access port (p) is dropped.

A Marlin unit operating in tandem mode may also operate on a per accessport and tag basis. In this case, the state relative a first access portand a first tag (p,t) may be active while the state of the Marlin unitmay be stand-by relative a second access port and a second tag (p′,t′)where either p=p′ or t=t′ may hold. When the Marlin unit is in theactive state, relative to the access port (p) and the tag (t), theMarlin unit operates exactly in the same manner as an ordinary Marlinunit i.e. it forwards data tagged with 0xpt, received from any of itsnetwork ports to port p and modifies the tag to read 0xt, and forwardsall ingress traffic received via access port p tagged with 0xt to bothof its network ports 258, 260 and modifies the tag to read 0xpt. When inthe stand-by state, relative to the access port (p) and tag (t), theMarlin unit by-passes all traffic tagged with 0xpt received via U1 ports258 or 260 unmodified to U2 for egress traffic and vice versa foringress traffic. Furthermore, ingress traffic received via access port(p) tagged with 0xt is dropped.

In this way, the tandem node provides a high degree of redundancybecause the network ports are duplicated, as is the case in any Marlinunit, the node itself is duplicated, and the access ports areduplicated. A protected access network may constructed by connectingunits (U) with dual network ports to the tandem nodes such that bothnetwork ports of the unit (U) are connected to the two ports of the sameport group of the tandem node. Any system can be connected to the accessside of a tandem node and be protected as long as it accepts data fromboth network ports and transmits all data received from the access portsto both network ports. Two systems that may support the concept withoutmodification are the Marlin units themselves and the ADVA units such asFSP150CP units. It should be noted that a complete sub-tree built fromMarlin or tandem units can be connected to a port group. It should alsobe noted that an unprotected chain built from Marlin units fulfills theabove requirements and can thus be connected to a port group.

With reference to FIG. 4, it is possible to insert a header 62, such asa shim header, between a source address 64 and an Ethernet type ETYPE 66of a typical 802.1q frame format 68 such as IEEE 802.3.

As shown in FIG. 5, the Marlin unit of the present system may use a 32bit shim header or tag 70 based on the IEEE 802.1q format that ispositioned immediately after a source address 72 of an IEEE 802.3Ethernet packet 76.

The tag 70 may include a TPID field 78, priority field 80, CFI field 82and a VID field 84. The 12 bit VLAN ID field (VID) 84 may be dividedinto three independent 4-bit fields such as a nibble 86, nibble 88 andnibble 90 used for storing the source routing information. This resultsin up to three multiplexor levels per 802.1q header. More levels may beused but requires the router to process multiple 802.1q headers to map acustomer port to a virtual interface that is QinQ. The Marlin unit usesthe VID (VLAN Id) field 84 of the tag for addressing and forwarding ofpackets through the unit. Preferably, the TPID section 78 is always setto 0x8100. The priority field 80 may be used for prioritization ofpackets. The CFI field 82 is usually not used by the Marlin unit and ispreferably always set to zero.

As indicated above, the 12-bit VID field 84 may divided into the nibbles86, 88, and 90 where each nibble is used for addressing in one level ina Marlin tree topology. When addressing in a tree topology, the firstnon-zero nibble (starting with nibble 86) indicates the address for thefirst unit the packet arrives to. The next nibble, such as nibbles 88,90 if any, indicates the address for the next unit down or up in thetree hierarchy of nodes.

FIG. 6 shows an example 92 of how the tag addressing may be done in atree topology. FIG. 7 defines rules 93 for valid addressing when theunit is in the tree mode or point-to-point mode.

As shown in FIG. 8, ring/daisy-chain addressing 95 has two nibbles ofthe VLAN tag that are used for one level of the ring. The first nibbleis used for ring-node number addressing. The second nibble is used foraddress port in the ring-node. This leaves one nibble that can be usedfor addressing in one additional tree level. When addressing in a ringthe first non-zero nibble, starting with nibble 90, indicates ring-nodenumber and the following nibble indicates the port address.

FIG. 9 shows how addressing in a ring topology 97 may be done and FIG.10 defines rules 99 for valid addressing when the unit is in ring-mode.Port 0xE is used for ring topology detection and is described in thetopology detection paragraph.

Each access port, such as ports 58, 60, may be in branch or leaf mode toindicate if the port is connected to another marlin node unit or to acustomer. When the node is in the branch mode and a tag is present thetag is modified with the arriving port number. When the node is in thebranch mode and no tag is present, a new tag is added in the same manneras if the node where in leaf mode as described below. When the node isin the leaf mode, which may be the default mode, a new tag is alwaysadded to the arriving frames. A new 802.1q shim header is added topackets that arrive on the port independently of the packet content. The12-bit tag is set to the branch mode hex (00X) where (X) corresponds tothe port number 1..A. When the node is in the branch mode, the uplink ofanother marlin unit is attached to this port. Arriving ingress packetsthat already contain a marlin specific 802.1q shim header are modifiedto include both the port information from the previous unit(s) and theport info from this unit. The 12-bit tag is therefore set to hex (0YZ)where (Y) corresponds to added port number.

With reference to FIG. 11, when a packet arrives on an access port thatis set in the leaf mode a VLAN tag 108 is added to the packet. The nodeadds the port number to the VID field 108 of the tag so that a packetarriving to port 4 will have the VID field set to 0x004. Packetscontaining VLAN tags and arriving to access ports when the node is inthe branch mode will have their tag modified. The port number at whichthe packet arrives on is added to the tag on the first empty or zeronibble in the tag, starting with, for example, the rightmost nibble. Inthis way, an ingress packet with tag VID 0x004 arriving on port 2 willbe forwarded to the network port with tag VID 0x042. Packets withoutVLAN tags arriving to access ports when the node is in the branch modeare treated in the same way as packets arriving to access ports when thenode in the leaf mode. Access ports can be set to U1/U2/both mode. If anaccess port is set to U1, packets from this port will only be forwardedto network uplink ports U1. If an access port is set to U2, packets fromthis port will only be forwarded to network uplink ports U2. If anaccess port is set to both, packets from this port will be forwarded toboth network ports U1 and U2. Preferably, OAM replies are always sentback via the same port as the request arrived via, regardless of theU1/U2/both setting.

For example, a packet 100 may arrive from a customer 102 to an accessport 104 of a node 106 that is in a leaf mode 105 which means the nodeis located at the lowest level of a node tree 99. If the node 106 is inthe branch mode, it is presumed that the packet already has a tag andthat a previous node in the leaf mode lower down in the tree has alreadyadded the tag with the VID field. Since the node 106 is in the leafmode, the node 106 adds an empty tag 107 to the packet 100 with the VIDfield 108 and the nibble furthest to the right is filled in with theport number at which the packet 100 arrived. For example, the VID field108 of the packet 100 may have nibbles 110, 112, 114. If the packet 100arrives on port 4, the nibble 114 will be set to 4 so that the VID field108 may read 0x004 before it is sent further up in the node tree 99.When the node 106 forwards the packet to a node 116 that is in a branchmode 117, the information in the VID field 108 is shifted one step tothe left. If the packet 100 arrives on network port 2 of the node 116,the nibble 112 is modified to include the number 4, to illustrate theport number on a first node level 118 and the nibble 114 will modifiedto include the number 2 to illustrate the port number on a second nodelevel 120 so that the VID field 108 reads 0x042. In this way, the portnumber of the nibble 114 is shifted to the nibble 112 while the nibble114 receives the new port number of the node at the higher level of thetree topology 99.

When the node 116 forwards the packet to a node 122, the information inthe VID field 018 is again shifted one step to the left. If the packet100 arrives on access port 3 of the node 122, the nibble 110 will bemodified to include the number 4, the nibble 112 will be modified toinclude the number 2 and the nibble 114 will be modified to include thenumber 3 to illustrate the port number on a third node level 124 so thatthe VID field 108 reads 0x423. The node 122 then sends the packet 100 toa router or a switch 123 that may send the information to the desiredaddress of a network core system. If the router or switch 123 noticesthat the VID field 108 is not configured correctly, the router or switch123 may be set to drop the packet.

With reference to FIG. 12, when a tagged packet arrives on a networkport, i.e. an egress arrival, its destination is defined by the firstnon-zero nibble in the VID field of the VLAN tag. It should be notedthat the VID field does not include an address of the final customer,only the port number of the leaf node to which the customer isconnected. If the first non-zero nibble is 0x1-0xA, the packet isforwarded to the queue for the corresponding port. The tag is alsomodified so that the first non-zero nibble is set to 0. If only the lastnibble is non-zero the VLAN tag is removed since the packet has reachedits final destination through the tree topology. Untagged EFM OAM framesmay be forwarded to the OAM function of the unit.

For example, a packet 130 may arrive on a link 132 to the node 122 froma router 134. Before sending the packet into the node tree 101, therouter 134 adds the tag and the correct VID field information, accordingto a router table, and the path through the node tree 101. Either therouter and/or the node may verify that the added tag is configuredcorrectly. If the tag is not configured correctly, the packet may bedropped. The packet may receive a VID field 136 that reads 0x423. Thenode 122 first reads the number in the nibble 142. Before sending thepacket 130 via port number 3, the port number is then removed and theVID information is shifted one step to the right so that the VID field136 reads 0x042. The node 116 that is linked to port 3 of the node 122receives the packet 130. The node 116 first reads the number in thenibble 142. Before sending the packet 130 via port number 2, the portnumber in the nibble 142 is removed and the VID information is againshifted one step to the right so that the VID field 136 now reads 0x004.The node 106 that is linked to port 2 of the node 116 receives thepacket 130. The node 106 first reads the number in the nibble 142.Before sending the packet 130 via port number 4 to the customer 102, theentire tag including VID field is removed, since only the last nibble isnon-zero.

As best shown in FIG. 13, it is possible to construct trees with up tothree levels so that an unprotected tree topology 380 may beconstructed. The top Marlin unit 382 is connected to the routers 384,386. In this way, the number of customers that can be connectedincreases substantially.

As best shown in FIG. 14, the Marlin units can be deployed in a daisychain topology 388 where one network port 390 of a first Marlin unit 392is connected to a network port 394 on another Marlin unit 396 and so on.A first portion of the tag may address the Marlin unit on the chainwhile a second portion of the tag may address the port on the Marlinunit. In this way, a Marlin unit will forward the information betweenthe network ports as long as it is not the Marlin unit referred to inthe first portion of the tag. When a Marlin unit receives informationinto one of the access ports, the Marlin unit may add the first portionof the tag the number of the Marlin unit on the chain and a secondportion of the tag the number of the port number from which theinformation was received. The Marlin unit will then forward theinformation in both up-links, as described above. Up to 12 units can beconnected in a single chain. Of course, more or fewer units may be usedas required. It is also possible to support router redundancy in a chainby connecting the same or two independent routers 398, 400 to the twoend-points 402, 404 of the chain. If the chain breaks egress traffic toa chain node arriving to the router on the other wrong side of the breakmay be lost and the system may never recover. Some customers may stillhave service in this scenario.

This is a problem related to VRRP/HSRP and is in principle identical tothe problem discussed above in relation to the tandem node. Othermechanisms, such as OSPF, may recover completely even after the chainbreaks. VRRP/HSRP provides router redundancy and provides protection ofthe link connected directly to the router port but may not reliablyrecover from other failures.

As best shown in FIG. 15, the Marlin units 406, 408 can be connected ina point-to-point topology 410 by connecting the network port 412 of theunit 406 to the network port 414 of the other unit 408. The customers409 are connected to the unit 406 and the customers 411 are connected tothe unit 408.

A protected tree topology may be constructed by using tandem nodes inthe same manner as unprotected trees are constructed from the Marlinunits. A tandem node is a protected tree. A multi-level protected treemay be constructed by connecting both the network ports of a Marlinunit, or a tandem node, to the two ports of a port group of a tandemnode.

The following requirement may be placed on protected trees. A tree isprotected at level (i) only if it is also protected at level (i−1). Thisrequirement implies that protected trees are built top-down startingfrom the root. For example, if the second level is constructed usingTandem nodes, then so is the first level. Examples of redundant treetopologies are given in the figures below.

FIG. 16 shows a redundant tree topology 416 where the top level isconstructed using a tandem node 418 that includes the single nodes 418 aand 418 b. Preferably, each tree topology has only one top node that isdirectly connected to the routers 419, 421. In this way, the tandem node418 may have an network link 460 connected to the router 419 whileanother network link 462 is connected to the router 421. The tandem node418 has also pairs of access links 464, 466, 468, one from each node 418a and 418 b, connected to the nodes 470, 472, 474, respectively.

In FIG. 17 a tree topology 420 is shown wherein also the second level isbuilt using redundant tandem nodes 422, 424, 426. Router redundancy maybe supported in protected trees in exactly the same way as inunprotected trees i.e. by connecting dual redundant routers to the dualuplinks of the protected tree.

As best shown in FIG. 18, a protected chain topology 428 is constructedby connecting to the uplinks 430, 432 of an unprotected chain 434 to thetwo ports 436, 438, respectively, of a port group of a tandem node 440that includes the single nodes 440 a, 440 b. The port 436 may beassociated with the node 440 a while the port 438 may be associated withthe node 440 b. Router redundancy may be provided by connecting two dualredundant routers 442, 444 to the two network ports of the tandem node440. Traffic that is received by the tandem node 440 will drop theinformation in one of the links 430, 432, depending upon which node isactive or in the stand-by mode, and the tandem node 418 sends theinformation in both up-links 441, 443. For example, when the node 440 ais in the active state and the node 440 b is in the stand-by state, thenode 440 b will drop traffic received in the port 438 connect to theaccess link 432. The active node 440 a will send the informationreceived from the link 430 via the uplink 441 to the router 442 and viaa second uplink connected to the stand-by node 440 b that forwards theinformation via the uplink link 443 to the router 444. Traffic that isreceived by the tandem node 440 will be sent in either link 430 or link432 to the chain 434, as explained above.

As shown in FIG. 19, when two uplinks 446, 448 are used inpoint-to-point configuration 450 data is always sent on both links. Itshould be noted that the configuration 450 has no routers. For example,the unit 452 may send on both links 446, 448. On the receiver side, suchas the unit 454, data is accepted from one of the links 446, 448. Theunits may automatically select one of the uplink ports from which toreceive data. The units may automatically switch over to the other linkon the receive side in case of failure on the active link.

While the present invention has been described in accordance withpreferred compositions and embodiments, it is to be understood thatcertain substitutions and alterations may be made thereto withoutdeparting from the spirit and scope of the following claims.

1. A method of sending information through a physical topology,comprising: providing the physical topology with a first node and asecond node, the first node having a first access port, a second accessport and a first uplink connected to a router, the first access porthaving a first port number and the second access port having a secondport number; the second node having a first access port and a firstuplink, the first uplink of the second node being connected to the firstaccess port of the first node, the first access port of the second nodehaving a third port number; providing a third node having a first accessport and a first uplink, the first uplink of the third node beingconnected to the second access port of the first node; sending a firstpacket via the first access port to the second node, the first packethaving a tag having a first nibble field and a second nibble field; thesecond node adding the third a port number of the first access port ofthe second node to the first nibble field of the first packet; thesecond node sending the first packet via the first uplink of the secondnode to the first access port of the first node; the first nodereceiving the first packet via the first access port of the first node;the first node adding the first port number of the first access port ofthe first node to the first or second nibble field of the tag adjacentto the third port number; and the first node sending the first packetvia the first uplink of the first node to a first router.
 2. The methodaccording to claim 1 wherein the method further comprises providing thefirst node with a second uplink connected to a first sister node, thefirst sister node being identical to the first node.
 3. The methodaccording to claim 2 wherein the method further comprises, the firstnode sending the first packet via the second uplink to the first sisternode.
 4. The method according to claim 3 wherein the method furthercomprises the first sister node sending the first packet via a firstuplink of the first sister node to a second router.
 5. The methodaccording to claim 1 wherein the method further comprises determiningwhether the first nibble field is a first non-empty nibble.
 6. Themethod according to claim 5 wherein the method further comprisesdetermining whether the first node is in a leaf mode or in a branchmode.
 7. The method according to claim 6 wherein the method furthercomprises always adding a new tag when the first node is in the leafmode.
 8. The method according to claim 1 wherein the method furthercomprises the second node removing a port number stored in a firstnibble field of a second packet.
 9. The method according to claim 8wherein the method further comprises the second node removing the portnumber from the first nibble field when the first nibble field isnon-empty.
 10. The method according to claim 1 wherein the methodfurther comprises forming a tree topology of nodes connected to oneanother.
 11. The method according to claim 1 wherein the method furthercomprises forming a ring topology of nodes connected to one another. 12.A method of sending information through a physical topology, comprising:providing the physical topology with a first node and a second node, thefirst node having a first access port, a second access port and a firstuplink connected to a router, the second node having a first access portand a first uplink, the first uplink of the second node being connectedto the first access port of the first node; sending a first packet in anegress direction from the router via the first uplink to the first node,the first packet having a tag having a first nibble field and a secondnibble field; the first node reading a port number in the first nibblefield; the first node removing the port number in the first nibble fieldof the first packet; the first node sending the first packet to thesecond node; the second node reading the port number in the secondnibble; the second node removing the port number in the second nibble;the second node sending the first packet, via the port number read inthe second nibble, to a destination device.
 13. The method according toclaim 12 wherein the method further comprises the first node sending thefirst packet, via the port number read in the first nibble, to thesecond node.